In recent years, radio frequency identification (RFID) systems based on RFID have been under study in various fields such as physical distribution.
An RF tag used in the RFID system has an antenna and an IC chip. The RF tag receives a radio wave (carrier wave) transmitted from an antenna of a reader at the antenna thereof. The RF tag then transmits, on a reflection wave, identification data or the like on an object being conveyed recorded in the IC chip back to the reader. In this way, the RF tag can communicate with the reader without the need of touching the reader. The reader may have a writing function for writing information to the RF tag.
In Patent Literature 1, as an antenna for the RF tag, a patch antenna is described in which a plate-shaped radiating element and a conductive ground plate are arranged on the front surface and the back surface of a dielectric substrate, respectively. In Patent Literature 2, a thin patch antenna is described in which a magnetic sheet is disposed between an antenna part and a conductive ground plate, and the conductive ground plate is in contact with a metal member via a substrate.